I have followed the directions in the manual but am encountering the following error when trying to use the plugin.
Fatal error: Cannot instantiate non-existent class: geshi in (path)/syntax_hilite.php on line 31
Any thoughts?

Have you followed the directions in the Manual word-to-word?
The syntax_hilite.php file should be in your plugins directory.
Before activating the plugin, change $pPath variable to the physical path to the directory(wp-includes recommended) where you uploaded the geshi directory & geshi.php, also note that relative paths won’t work.

Yes I followed the directions in the manual word for word.
The syntax_hilite.php file was in my plugins directory and was activated. I changed $pPath however I may have messed this step up, as I don’t comletely understand physical path. Lets say that the geshi.php and geshi directory are in http://davidblog.ws/blog/wp-content/. What should this line be.
I have a feeling I have it correct at the moment because otherwise I recieve many more errors on all of my blog pages. But who knows, I am pretty slow sometimes.

The site’s not coming up for me, either. The domain name isn’t resolving in my browser, nor can I ping it. It just times out.
Looks like your site’s either down, or a router is down between me and your site.

Name this file as path.php & place it the same directory where you have placed geshi.php & the geshi directory. Call this file in the browser. So if you have placed this file in the wp-contents directory, then you call it as http://davidblog.ws/blog/wp-content/path.php Copy whatever the file outputs on screen, & remove path.php from its end. Now you have the physical path of the directory where geshi.php & geshi directory resides. Place this path in the $pPath variable of your syntax_hilite.php file. Just make sure that it has no spaces at either end of it & it ends with a trailing slash(/).@benramsey:-
Looks like your site’s either down, or a router is down between me and your site.

The site isn’t down or I would have known. I’ve got 5 website monitoring services checking on it all the time. 🙂 Looks there’s a problem with the router between you & the website.

Also, is there a way you can add in functionality to make optional the prefix “CSS:” or “HTML:” for the block of code being hilited? I really hate that big, bold “CSS:” that automatically gets stuck before my code. I mean, if I’m talking about CSS, it’s obviously going to be CSS in the code block – no need to reiterate.